1. Field of the Invention
The present invention relates to a flow rate verification failure diagnosis apparatus, a flow rate verification failure diagnosis system, a flow rate verification failure diagnosis method, and a control program product for flow rate verification failure diagnosis.
2. Description of Related Art
In a film deposition device or a dry etching device in a semiconductor manufacturing process, special gas such as silane or phosphine, corrosive gas such as chlorinated gas, combustible gas such as hydrogen gas, or the like are used.
Flow rates of these gases should strictly be controlled.
The reason of this is because the gas flow rate directly affects a quality of the process. Specifically, the gas flow rate greatly affects a film quality in a film deposition process or a quality of a circuit processing in an etching process, whereby a yield of a semiconductor product is determined according to precision of the gas flow rate.
Another reason is that most of these gases are harmful to a human body and environment or have explosiveness. These gases are not allowed to be directly disposed in the atmosphere after they are used, so that a device used in a semiconductor manufacturing process should be provided with detoxifying device in accordance with a type of gas. However, the detoxifying device described above has limited processing capacity in general. Therefore, when the flow rate more than the allowable value flows, it cannot perfectly process the gas, so that the deleterious gas might be flown out in the atmosphere or the detoxifying device might be broken.
Moreover, since these gases, especially high-purity dust-free gas that can be used in a semiconductor manufacturing process, are expensive, and limitation is imposed on some gases for their use due to natural deterioration, they cannot be preserved in a large quantity.
In view of this, a known mass flow controller serving as a flow rate control device has conventionally been mounted in a semiconductor manufacturing process circuit so that a gas flows in an optimum flow rate for every type of gas. The mass flow controller described above changes the set flow rate by changing the applied voltage thus responding to changes in a process recipe.
However, these gases used in the semiconductor manufacturing process, especially the material gas for the film deposition among the so-called process gases, might cause precipitation of solid substances in a gas line due to its characteristics, so that the flow volume might be changed. The mass flow controller is formed with a capillary tube inside in order to supply a fixed flow rate with high precision. Even a small amount of precipitation of the solid substance on this portion could deteriorate the flow precision of the gas to be supplied. Further, since a gas with high corrosivity for an etching processor the like is flown, the corrosion of the mass flow controller cannot be avoided even if a material having a high corrosion resistance such as a stainless material or the like is used. As a result, a secular deterioration could occur, deteriorating the flow precision.
As described above, in the mass flow controller, the relationship between the applied voltage and the actual flow rate changes, so that the actual flow rate might possibly change. Therefore, the mass flow controller needs to be periodically subject to flow rate verification and calibration.
The flow rate verification of the mass flow controller is basically performed by using a film flowmeter. However, this measurement is performed with a part of a pipe removed. After the measurement, the pipe should be assembled in the original state, and a leakage check should be executed. Therefore, the work is very time-consuming.
Accordingly, it is ideal that the flow rate verification can be executed without removing the pipe.
One of methods of performing a flow rate verification in a state where pipes are assembled is disclosed in Japanese Unexamined Patent Application Publication No. 2006-337346. FIG. 11 is a schematic configuration diagram of a conventional flow rate verification system 100.
In the conventional flow rate verification system 100, a gas passage 103 is provided between a first shutoff valve 101 and a second shutoff valve 102, and process gas whose flow rate is adjusted by a mass flow controller 110 is supplied to a process chamber 111. The gas passage 103 is communicated with an inlet of a vacuum pump 104 via a discharge passage 105. In the discharge passage 105, a third shutoff valve 106, a temperature sensor 108, a pressure sensor 107, and a fourth shutoff valve 109 are disposed. The flow rate verification system 100 has a verification controller connected to the devices 106, 107, 108, and 109 for storing compression factor data peculiar to gaseous species and a value of volume of a predetermined space defined by an outlet of the mass flow controller 110 and the second and fourth shutoff valves 102 and 109.
At first measurement time, the flow rate verification system 100 obtains a mass G1 from a pressure P1 measured by the pressure sensor 107, a temperature T1 measured by the temperature sensor 108, a first compression factor Z1 corresponding to the pressure P1 and the temperature T1, and a volume V indicated with a broken line in the diagram. At second measurement time, the flow rate verification system 100 obtains a mass G2 from a pressure P2 measured by the pressure sensor 107, a temperature T2 measured by the temperature sensor 108, a second compression factor Z2 corresponding to the pressure P2 and the temperature T2, and the volume V. The flow rate verification system 100 obtains difference between the mass G1 at the first measurement time and the mass G2 at the second measurement time and verifies the flow rate of the mass flow controller 110 on the basis of the difference.
The above mentioned flow rate verification system 100 performs a flow rate verification using gas actually used for processing and corrects measurement values with factors peculiar to the gaseous species. Thus, the flow rate verification precision is high.
However, the conventional flow rate verification system 100 performs the flow rate verification on the basis of measurement results of the pressure sensor 107 and the temperature sensor 108 disposed in a gas box. Even in a case where it is determined that there is abnormality in the flow rate verification result, cause of the abnormality is not limited to the mass flow controller 110 while the flow rate verification is underway. There are cases that the cause of the abnormality is a failure in the pressure sensor 107 or disturbance (such as a temperature change in the gas box). The conventional flow rate verification system 100 does not have measures for verifying probability of occurrence of abnormality in the flow rate of the mass flow controller while the flow rate verification is underway. Consequently, in the conventional flow rate verification system 100, the pipes and the like have to be taken from the mass flow controller 110, and the mass flow controller 110 has to be taken from the gas box in order to diagnose failure in each of the devices. The failure test cannot be performed under the same conditions as those when the flow rate verification system 100 detects the flow rate abnormality. It cannot therefore discriminate between the case where the flow rate abnormality is caused only by a failure in the mass flow controller 110 while the flow rate verification is underway and the case where the flow rate abnormality is caused by a failure in another device configuring the flow rate verification system 100. Therefore, in the conventional flow rate verification system 100, when the flow rate abnormality is detected, the cause of the flow rate abnormality is not limited to abnormality in the mass flow controller 110 while the flow rate verification is underway. Thus, the reliability of the flow rate verification is low.